1. Field of the Invention
This invention relates to touch sensor array systems for deriving signals which represent any position selected by touch, for example through finger contact or by a stylus, in a given two dimensional area.
Such a system may be used as an overlay for the display screen of an LC or other display device to provide for example selected inputs to a display or other system in accordance with touched positions in the sensor array. In another example, the system may be used as a stand-alone graphics tablet connected to a computer system for enabling a user to enter information based on graphical representations drawn on the sensor array.
2. Description of the Related Art
Various kinds of touch sensor array systems are known. In one known arrangement, the system uses light emitters and light sensors positioned around the periphery of a sensing area. The emitters produced an X-Y grid of light beams directed onto the light sensors. When these beams are interrupted, for example by a person's finger, the position of the interruption is determined by sensing a change in the outputs of the light sensors affected.
In another known arrangement, sets of conductive strips extend at right angles to each other over a sensing area. The strips of the two sets are normally spaced but pressure at any point by a person's finger causes a conductor of one set to contact a conductor of the other set, the two conductors thus contacting being indicative of the location of that point.
In another kind of touch sensor array system, capacitive effects are utilised. In an example, pairs of spaced conductive strips or pads are provided which can either be physically displaced with respect to one another in response to finger pressure so as to alter the capacitance therebetween or capacitively coupled together in response to proximity of a user's finger.
The above known kinds of systems typically have only limited resolution capabilities. Moreover, these known arrangements rely in operation on a simple scanning drive scheme which means that for a touched position to be sensed, the actual touching must coincide with the scanning of the sensor element concerned.
It is an object of the present invention to provide a touch sensor array system which is capable of high resolution.